Objective: Olfactory dysfunction can be seen secondary to various diseases, such as sinonasal disease, infections of the upper respiratory tract, head trauma, and neurodegenerative diseases. A small number of recent studies have focused on olfactory dysfunction in different neuropsychiatric disorders. This study aimed to investigate olfactory bulb (OB) volume in patients with chronic major depression, as diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). In particular, we investigated patients treated with selective serotonin reuptake inhibitors (SSRIs). To the best of our knowledge, this is the first study to investigate this subject.